1. Field
This application relates generally to wireless communication and more specifically, but not exclusively, to synchronization of wirelessly transmitted information.
2. Introduction
A signal processing system may include several components that perform their tasks in a synchronized manner. For example, in a multi-channel audio system a given sample of an audio stream for one channel is output at substantially the same time as a corresponding sample of an audio stream for another channel. Also, in a control system, activation of one component may occur at a certain time with respect to the activation of another component. Similarly, in a monitoring system, sensing of one condition may occur at a certain time with respect to the sensing of another condition.
Synchronization may be readily achieved in cases where the components of a system are physically connected. An example of such synchronization will be described in the context of a wired stereo headphone set. The headphone set receives audio signals from a host device (e.g., a music player) and outputs the received audio signals via two earpieces in a synchronous manner. The synchronization between earpieces is measured by skew, which is defined as the relative latency between the left and right channels. It is desirable to keep the skew relatively small to provide good sound reproduction. For example, skew in excess of approximately 4-11 μs skew may be perceptible by a human listener. Providing a such small skew is readily achievable in a case where the two earpieces of a wireless stereo headphone are physically connected (e.g., where audio signals are delivered to the earpieces via a set of wires from the host device) since the signals for each channel may travel over identical signal paths and may be processed in a deterministic manner by each earpiece.
It may be more difficult, however, to achieve a desired level of synchronization in cases where the components of a system are not physically connected. As an example, in an audio system that uses wireless earpieces, the signals destined for each earpiece may not be processed in a deterministic manner by each earpiece. For example, the processing of received signals at each earpiece may take a different amount of time under different conditions (e.g., different channel conditions). Consequently, it may be more difficult to ensure that the audio output by one earpiece at a given point in time properly corresponds to the audio output by the other earpiece. Similar issues may arise in other types of wireless systems (e.g., control and monitoring systems). In view of the above, a need exists for effective synchronization techniques for signal processing systems.